Measurement instrumentation often involves the mounting of a sensor to a surface to be measured. The parameters to be measured vary with the field of interest and sensing transducer employed, yet common to many applications is the need to mechanically affix or position a sensor to a non-porous surface to be measured. For specialized conditions the sensor (such as a strain gauge) can be bonded directly to the surface to be measured. For many cases, however, the surface must be undisturbed after measurement. Such is the case of measurement of computer displays measured by colorimeters.
Colorimeters are devices for measuring the spectral content of light, where the measured light can be emitted either directly or indirectly from a given source. Recent developments have produced designs resulting in low cost colorimeters with performance characteristics approaching or exceeding professional quality required by the standards. One such colorimeter design is described in detail in U.S. Pat. No. 5,892,585, which is herein incorporated by reference in its entirety. With such cost effective, high-performance colorimeter designs available, a need has arisen for techniques for effectively mounting the colorimeter to the device being measured. In more detail, the physical factors relating to mounting a calorimeter to a target device present a number of non-trivial problems.
For instance, it is necessary to ensure that the forces of attachment are minimized to reduce pressure applied to a computer having a liquid crystal display (LCD). Otherwise, color distortion or damage to the LCD will occur. Also, LCD screens are particularly sensitive to the distribution and magnitude of the mounting forces. Thus, it is desirable that the calorimeter be relatively easy to position and attach to the target device. In addition, it is necessary to shield the measuring system from extraneous light (light from sources other than the target device being measured), which will otherwise reduce the signal-to-noise (SNR) ratio of the calorimeter system.
One conventional calorimeter design employs a strap or hanging apparatus for securing or otherwise suspending the colorimeter in front of a display screen. A donut-shaped foam pad or similar soft pad is used to keep the colorimeter from pressing too hard on the screen so as to prevent color distortion. However, such designs are cumbersome to use due to the nature of the strap or hanging apparatus, and generally provide a significant impediment to simple user operation. Moreover, such designs may not operate to maximize the SNR of the colorimeter device, particularly those designs where the colorimeter's peripheral field of view is not limited.
Other conventional designs employ one to four relatively large suction cups to hold the calorimeter in place. One such device uses a large annular suction cup fitted about a color sensor, where the sensor measures through the center. Another such design uses a large rubber suction cup with a rigid clear member through which a proximate sensor can measure. Another such embodiment employs four large suction cups, one at each corner of the sensing device. These suction cup methods each suffer from reliability issues.
For example, if the seal fails due to an imperfection in materials or a particle of dust or debris, then air will leak into the cavity causing that suction cup to fail. With just one suction cup, the device will simply fall off the target being measured. With the four corner type design, the weight of the device will be unevenly distributed, thereby causing a shift in alignment of the device and/or the failure of the remaining seals. This problem is further exacerbated in that displays have a tendency to attract dust. Moreover, the suction cups used in such designs have a relatively large depth. As a result, a slow air leak will cause the distance between the screen and sensor to substantially increase, thereby adversely affecting device measurement accuracy.
What is needed, therefore, are improved techniques for mounting a colorimeter to a target screen.